The Characteristics of Lithofacies and Depositional Model of Fine-Grained Sedimentary Rocks in the Ordos Basin, China

In order to clarify the characteristics of fine-grained sedimentary lithofacies and depositional models in lacustrine environments Chang 7 Member Upper Triassic Yanchang Formation Ordos Basin, we focus on classification controlling factors. Based typical field sections southern combined with methods organic geochemical analysis, polarizing microscopic observation, XRD elemental geochemistry, summarize main factors under different establish model backgrounds. Results show that Basin includes six major types, i.e., quasi-laminated clayey shale facies, blocky silty mudstone laminated mixed argillaceous siltstone facies. Al2O3, MgO, CaO, Na2O, K2O, SiO2 are relatively depleted, while TiO2, TFe2O3, P2O5 enriched 72+3. Meanwhile, trace elements Cd, Cu, Mo, U, V. The facies were influenced by various environments, such as paleoclimate, redox conditions, productivity terrigenous input. According types genetic mechanisms study area, two assemblages identified. rapid rise lake level during deposition 72+3 resulted an anoxic water column, high productivity, low input a humid climate weak-to-moderate weathering conditions. Therefore, assemblage is developed lower Member.